Some 200 civilians are trapped in a mosque in a suburb of the Syrian capital, according to the country’s Western-backed opposition.

Meanwhile, Syrian activists said mortar shells landed in three separate Damascus districts, killing one person and wounding several others.

The attacks coincided with Syrian army strikes on the Yarmouk camp for Palestinian refugees on the edge of the city, according to the Britain-based Syrian Observatory for Human Rights.

The violence came as US officials said Israel targeted advanced anti-ship cruise missiles near Syria's principal port city in an airstrike earlier this month, according to a report by The New York Times.

It cited the officials as saying the attack on July 5 near Latakia targeted a type of Russian-made missile called the Yakhont that Russia had sold to the Syrian government.

There was no immediate comment from President Bashar al Assad's government, whose key political ally and arms supplier is Russia.

The Syrian Coalition called on the United Nations in a statement to send "a strong warning" to Assad that he "must immediately release" the civilians trapped in the mosque in the Damascus suburb of Qaboun.

It did not say if the 200 had sought refuge in the mosque or were already there praying when fighting began.

It warned that thousands of civilians in Qaboun could be "massacred" by Assad's army, as armoured vehicles and elite forces move into the neighbourhood.

The Observatory said fighting in Qaboun that began after midnight had caused casualties.